Li3Ni2TaO6: A novel rock salt superstructure phase with partial cation order

Abstract

The new phase Li₃Ni₂TaO₆ has a novel rock salt superstructure, a= 8.4259(3)Å, b= 5.9073(3)Å, c= 17.7329 Å, Fddd. Within the cubic-close-packed oxide array, Ta occupies one set of octahedral sites giving isolated TaO₆ octahedra which edge-share with Li/NiO₆ octahedra Li and Ni are distributed non-randomly over three other sets of octahedral sites with Li : Ni occupancy ratios of 0.73 : 0.27, 0.59 : 0.41 and 0.55 : 0.45, respectively The higher Li : Ni ratio of the first set, 0.73 : 0.27 may be associated with cation-cation repulsion effects since this site is closest to Ta. Li₃Ni₂TaO₆ is a very modest semiconductor with conductivity of ca. 4 × 10^–6Ω^–1 cm^–1 at 300 °C and activation energy 0.77 eV, the disorder in the Li⁺ site occupancy is, therefore, static and does not yield significant levels of Li⁺ ion conductivity.